[Fix]修复持仓价格计算可能出错的bug
[Fix]修复持仓价格计算可能出错的bug

msincenselee/vnpy,rrrrrr8/vnpy,rrrrrr8/vnpy,msincenselee/vnpy,andrewchenshx/vnpy,harveywwu/vnpy,bigdig/vnpy,bigdig/vnpy,bigdig/vnpy,wisfern/vnpy,wisfern/vnpy,harveywwu/vnpy,wisfern/vnpy,rrrrrr8/vnpy,vnpy/vnpy,andrewchenshx/vnpy,wisfern/vnpy,msincenselee/vnpy,andrewchenshx/vnpy,msincenselee/vnpy,rrrrrr8/vnpy,bigdig/vnpy,harveywwu/vnpy,rrrrrr8/vnpy,rrrrrr8/vnpy,wisfern/vnpy,harveywwu/vnpy,andrewchenshx/vnpy,andrewchenshx/vnpy,vnpy/vnpy,harveywwu/vnpy,harveywwu/vnpy,wisfern/vnpy